relates to a test strip evaluating instrument for multiple test strips with a transport and positioning device by means of which the test strips are transported at right angles to their longitudinal direction from a test strip feed area along a transport path to a disposal area, in which at least one measuring station with an optical measuring unit is arranged on the transport path, rails on which the test strips slide running along the transport path, and at least two rows of cam elements following one another in the transport direction, the cam elements being driven synchronously with one another in a periodically recurring movement path such that they transport the test strips in a step-wise manner.
Multiple test strips are in common use for the analysis of materials to be tested, for example for the analysis of urine. These types of test strips have a plurality of adjacent, equally spaced test fields, which contain reagents in different combinations for determining various components of the sample. The test strips are usually dipped briefly into the material to be tested, e.g. urine. The reaction of the sample with the reagent leads to an optically detectable change, usually a color change, on the test fields. This change is evaluated visually or with a suitable evaluating instrument. Instruments for the evaluation of test strips are matched as regards their properties with the test strips of a particular manufacturer. The type of test strips used and a compatible evaluating instrument together can be considered to form a test strip analysis system.
High demands are made of test strip evaluating instruments. The evaluation of the optically detectable change on the test fields usually takes place by reflection photometry. The accuracy of the measurement is here largely dependent on the exact positioning of the test strips in relation to the optical measuring unit. Since there is a trend towards smaller and smaller test fields and only the central area of each test strip can be used for an accurate measurement, high demands have to be imposed on the positioning of the test strip with respect to the test field area. This involves the longitudinal and transverse positioning of the test strip. Particular importance attaches to the precise maintenance of the distance between the optical measuring unit and the test field surface (i.e., distance positioning), because the accuracy of the optical measurement depends on this distance to a very great extent.
A test strip evaluating instrument of the kind described in the preamble is known from EP-A-174 564 which corresponds to U.S. Pat. No. 4,689,202. The rails of this reference are part of a so-called base tray and run, interrupted by two reading station platforms, between a first depression in the sample feed area and a second depression in the disposal area.
The base tray comprises two longitudinal slots through which pegs serving as cam elements can penetrate from below the base tra up to and above the rails. The pegs are part of a test strip conveying element which follows a particular path, namely a closed curve in a vertical plane (vertical orbital path). This curve contains a horizontal path section, in which the pegs are situated in their topmost position and transport the test strips, and a roughly semi-circular-shaped path section in which the pegs, after completion of a transport step, are withdrawn downwards, run back and are raised again so that tiles project from below the base tray so as to extend above the rails behind the next test strip to be conveyed.
The accuracy of distance positioning is ensured in the case of the above-described previously known instrument by the fact that the test strips rest on the measurement platforms during the measurement and are pressed elastically against the latter from above. Particular importance is attached to the fact that the platforms have a plane surface at least in the region of the test fields. In addition the base tray has to be of stable overall design and be exactly positioned, in order to reasure the measuring accuracy.
The known device meets the requirements as to accuracy of the measurement. The design is, however, relatively complicated. Moreover, several parts of the instrument are contaminated by the material being tested, such as urine, during use. This applies particularly to the base tray and the test strip conveying element. In order to prevent the material being tested, particularly urine, from penetrating into the inside of the unit, both the base tray and the test strip conveying element have raised edges around their respective circumferences. Although the material being tested, e.g. urine, is thereby contained, it nevertheless collects on the planar surfaces of these elements. These surface therefore have to be cleaned thoroughly at regular intervals.
Transport of analysis elements by means of vertically mobile rails and horizontal transport elements is known from U.S. Pat. No. 3,645,690. The basic transport principle shown in this referencc. is also described as a "walking beam". The conveyor shown in this reference, having horizontally mobile transport elements, is located beneath the analysis elements. Furthermore, in this reference, no transport insert is provided, and the analysis elements described therein are not test strips of the type tested in the present invention. According to this reference, the analytical evaluation in that system takes place by transmission photometry, and accordingly the special requirements regarding positioning accuracy which are associated with reflection-photometric evaluation (as used in the present invention) do not therefore arise with the known apparatus shown in this reference.